No batteries required.
The guy drones on about the case before he mentions that it’s only has a 14 watt max output. That condition requires full sun full face on. All photovoltaic devices performance falls off rapidly to trickle charge levels.
His “testing” is subjective. If one pays $139 (Amazon price) one should at least invest in a $20 volt/amp meter to show real output.
Anker and others have 20 watt folding panels with 2 USB ports in the $60 range.
I have a 20W folder for camera batteries, Handi-Talk radio, and 10,000mAH battery packs. Need 6 hours full sun to charge the latter, rarely get that. Use car 12V accessory socket to fully charge it.
Bigger question raised is intended use. For occassional camping or hiking one is better off with the several battery packs for a third of the cost and far hardier in the field. Question of what one carries in the field; GPS unit, camera, USB flashlight. An I-Pad in the field??